A proxy server is an online tool that is generally used to mask a request made by a given computer system. Think of a proxy server as an online intermediary for any kind of online request, be it for web pages, files, et cetera. A proxy server is generally used for a vast variety of different reasons, but we will only discuss a few of the most common ones below.
First, a proxy server is often employed for security purposes. A user can download or scan a file, webpage, or other online document for viruses and other malware via proxy server, and if the files in question are infected, the computer that the user in question made the request from remains free from any such attacks. Indeed, a proxy server can be an incredibly useful tool for network security.
Proxy server technology is also used both to filter web content, and, paradoxically, to get around web filters and blacklists as well. For example, many private networks, such as those of various employers, will employ a web content filtering proxy server to keep their employees from visiting various undesirable sites while on the clock. However, on the flip side, political activists from areas where speech is restricted, as well as old fashioned computer criminals, often use open proxy servers to get around filtering software, or to cover the tracks of their online crimes.
Since a proxy server masks the IP address of the user who made the initial online request through it, the identity of proxy server users can often be difficult to discover. This tends to impair, if not thwart outright, any attempts by internet security experts or law enforcement to catch computer criminals. While proxy servers can be amazingly efficient at preserving network security, less than savory types have been known to use proxy server technology for more nefarious ends. Always have an up to date spyware, malware, and virus scanner running on your computer, and be aware of what can happen online.